Quit: V-belts, pulleys, tensioners ??? 2,5 TD

Hello, I have a quit in the stand, which comes from the V-belt (or what is driven from it). Today I changed the tensioner, but it was not. Quits still cheerfully ahead of me. I have seen that there is still something like a tensioner on the alternator, can that come from it? Then I have found that if I make the wedge belt tighter by using the small shock absorber from the tensioner pressure that Quits go away. Is my tensioner with Or can it only lie on the V-belt? Greetings Dieter